As Epic puts it: They released the new version of Unreal Engine 4. I mean literally they released everything(also on github)...the source is available and all Operating systems and more are supported.

Unreal Engine 4 is available for Linux, Windows, XBox One, Playstation 4, Mac OS x, Android, iOS, HTML5(Yes you can directly run a game anywhere through the webbrowser, streaming from anywhere(any hardware, any OS.) and myriad other platforms.

This is not really a big deal, previous engines too supported supported similar universal operating environments. What makes this different is pushing for adoption, coherency and steadiness in development of software universally for all the platforms.

Note: Only a matter of time before Crytek supports Cryengine for linux.